In U.S. patent application Ser. No. 326,777 filed 20 Mar. 1989 of H. A. Leupold for "Method of Transforming a Passive Ferromagnetic Material Into a Permanent Magnet" and assigned to a common assignee, and with which this application is copending, a method is described in which superconducting persistent currents are induced in annular rings or current loops with the aid of a high permeability material such as iron. The method includes the steps of:
(A) encasing a bar of iron in an annular shell of a superconductive material at a temperature above the transition temperature of the superconductive material,
(B) placing the encased iron into an applied axial magnetic field providing sufficient oersteds to magnetize the iron thereby enclosing a large amount of flux in the superconducting shell,
(C) lowering the temperature to below the transition temperature of the superconductive material whereupon all of the enclosed flux is permanently trapped, and
(D) removing the applied axial magnetic field.
There are even higher permeability ferromagnet materials however, such as gadolinium that obtain such permeabilities only at low temperatures. For the method of Ser. No. 326,777 to work in such a case, the transition temperature of the encasing superconductive material must be even lower.